How to check IOB register packing?

Look in xilinx's map report file (*.mrp). Near the end there is a table with a row for each IO signal and its characteristics including what IOB registers are used (OFF - output flipflop, IFF - input flipflop, ODDR - output double datarate, IDDR - input double datarate, ENFF - tristate enable flipflop,....)

Here's an example of inferring tri-state IOs: assign EthMiiDat = EthMiiDatT ? 1'bZ: EthMiiDatO; assign EthMiiDatI = EthMiiDat;

The IO Pin is EthMiiDat. Three signals go to the FPGA fabric: EthMiiDatO is the output, EthMiiDatI is the input and EthMiiDatT is the tri-state enable.

Another way to verify this is to open the ncd file in FPGA_EDITOR and see what are put in the IOBs.

HTH, Jim

Or look at the pad report, there is a column there indicating whether the signal is registered or not for each pad.

Hi, In the map report file, all the input and output signals are listed under the IOB name column in the IOB properties section. But under the reg(s) column, only my clock outputs have the OFF1 entry and all other input and ouput signals have no entry of IFF/OFF/ENFF. What does it mean?

Me, I like to have an OFFSET OUT AFTER constraint that gives a Tco value slightly larger than the guaranteed clock-to-out time for my I/O standards. If I don't have a register packed in the IOB, there's a failure in the timing constraint.

It means that those IOs aren't registered in the IOB. If you want to figure out why, I suggest you search comp.arch.fpga.

Neat!

Or set static timing constratints on all pins that can only be reached with IOB FFs...

-- Phil Hays

Hi Phil, I am new to using these tools and designing with FPGA's. Can you tell me how to set static timing constraints on the pins that can only be reached with IOB FFs?

Thanks & Regards, Srini.

Hi Jim, I am able to see the flops packed into IOBs in FPGA editor. Thanks for your help.

Srini.

That's a good way to check...

This is my favorite. If timing passes, I know that the FFs that are supposed to be in the IOBs actually are. This has proved to be a very useful check.

Bob Perlman Cambrian Design Works